A machine tool includes at least one feed mechanism for making a workpiece and a tool move relative to each other. The motor for driving the feed mechanism is controlled by a numerical control device. When a feed direction of the workpiece or tool is reversed by the feed mechanism, the direction of action of frictional force between the relatively moving parts included in the feed mechanism (for example, the feed screw and nut) reverses, so the phenomenon arises of the operation of the feed mechanism being delayed for an instant. For example, when using two perpendicularly intersecting linear feed mechanisms to make a workpiece or tool move in an arc, this phenomenon of delay generally causes the unpreferable position error called “stick motion”.
In relation to this, there is known a numerical control device which is designed to update backlash correction command values in accordance with the elapsed time from the occurrence of reversal if the feed direction of the table carrying the workpiece reverses, to add the correction command values to the position command values, to use the results of addition as the basis to control operation of the servo motors which drive the table, to precisely compensate for elastic deformation which occurs when the feed direction reverses, and to suppress occurrence of stick motion (see PLT 1). Further, PLT 2 discloses to change the Y-axis servo parameters of speed loop gain and position loop gain in accordance with the X-axis position.    PLT 1: Japanese Unexamined Patent Publication No. 2004-234205A    PLT 2: Japanese Unexamined Patent Publication No. 6-297058A